Topics covered under Boundary Diagram.

It is a robust tool used in the creation of FMEA. It divides the boundary between the system under consideration called the design system and the system Surrounding the design system called the mating system/ Surrounding System.

It helps in capturing the elements outside the boundary, which may become a potential causes/ Effects of failure.

Also included are the Sub systems/ Components that need clearance from the system under consideration.

Boundary diagram is also helpful in identifying the factors hat need to be addressed in the FMEA.

Interface matrix:

How to create a Boundary Diagram?

To create a boundary diagram, you need to have a team of experts for the system under design consideration as well as the external system with which it has interfaces. First you create the boundary to include the system, in this case we are considering the following diagram

Boundary diagram example:

The most important part of the boundary diagram is the interface matrix. This is mostly the reason DFMEAs become more robust. There are two ways of creating interface matrices

One is done in the matrix form, outside the boundary diagram and other one is inside of the Boundary Diagram.

Second is creating the Attribute box, listing attributes of the design system. Next step is the most important reason, the reason why boundary diagram is created prior to DFMEA. The interface matrix can be created in two ways, interface matrix method and box method.

Lets consider both the ways independently, and use anyone which you feel comfortable with.

Interface matrix method: Template

A robustness tool used to highlight any component or system interactions
You should use the boundary diagram as an input to the Interface Matrix
The Interface Matrix is an input to the Potential Causes of Failure
Negative or Positive interactions are analyzed for corrective action recommendations if deemed to contribute to a Cause Failure Mode Mechanism.

Determine all of the components that are part of the system
Each component is listed on the horizontal and vertical axis of the matrix

Matrix form presentation

• Steps in creating an interface matrix.
• There are four types of interactions to be evaluated for each component – component intersection
• There four types of interactions are:
• Physically touching
• Exchanging information
• Transferring material
• Transferring energy

Positive and negative interactions

• Each type of interaction can either have a positive or a negative interaction
• Positive interactions are expected
• Negative interactions are unexpected
• Every interaction both positive and negative should be verified

Assign a value to it

• Assign a value for each interaction
• Each type of interaction is evaluated on a 5 level scale
• 2  Necessary for function
• 1  Beneficial, but not absolutely necessary for functionality
• 0  Does not affect functionality
• -1 Causes negative effects but does not prevent functionality
• -2  Must be prevented to achieve functionality
  

Example of interface matrix Type I:

In the second method of doing the interface matrix, we put boxes under the design system where we identify and document the interactions. These are same 4 kinds as previously identified. Now these are marked in form of arrows from one system to another system based on the interactions.

The rating system is same as above.

Example of interface matrix Type II:

How does this information from Boundary Diagram flow into the DFMEA ?

• You should use the boundary diagram as an input to the Interface Matrix.
• The Interface Matrix is an input to the Potential Causes of Failure.
• Negative or Positive interactions are analyzed for corrective action recommendations if deemed to contribute to a Cause Failure Mode Mechanism.

How does data Flow from the Boundary Diagram to the FMEA:

Why do we need Boundary Diagram?

Boundary diagram is an excellent tool which not only captures failures from the functionality of the product, but also failures likely to be caused due to improper/ undesired functioning of the sorrounding/ mating components. This also called as the interface matrix, captures the failure modes arising due to the failures passed from the failed mating component to the operating/ design component. When doing the DFMEA, we can ensure that the mating component to the design component does not cause the failure/ intereference in the cordial functioning of the Intended component.